The watch permanently tried to update the GPS Version, but after "successful" update, it was still in GPS version 4.15.
To get out of the "update-loop", i deleted GARMIN/REMOTESW/gup3799.gcd (according to the thread below) --- now the update-loop seems finished.
If i ask the watch for a software update, it finds nothing (both tested by bluetooth and wifi).
How can i update the watch to GPS Version 6.01?
(similar bug in: forums.garmin.com/sports-fitness/healthandwellness/f/venu-2/286597/8-11-update-shows-incorrect-gps-version)
(The bug occured first during a poor internet/wifi connection during a car ride)